As a measuring method for measuring a thickness of a thin film, a reflected light measuring method has been applied. FIG. 1 illustrates a diagram illustrating a basic structure of a reflected light measuring unit for measuring a thickness of a thin film of the related art.
As illustrated in FIG. 1, it is understood that the reflected light measuring unit for measuring a thickness of a thin film of the related art is substantially configured to include a light source 11, a beam splitter 2, a condensing lens 3, and a detector 4. Light is emitted from the light source 11 and the emitted light is split by the beam splitter 2 at a ratio of 50:50. Among split light, the reflected light is collected by the condensing lens 3 to be irradiated onto an object 1 to be measured.
The irradiated light is divided into light which is reflected from an upper layer of the object 1 to be measured and light which is reflected from a lower layer thereof and a phase difference between the light is measured and analyzed by the detector 4, thereby measuring the thickness of the thin film.
Further, a measuring method which simultaneously measures the thin film thickness and a surface profile has been actively researched. Specifically, as studies on a dispersive white-light interferometry, measurement of a surface profile and a thickness of a multilayered thin film has been reported by U. Schnell (U Schnell, R. Dandliker, and S. Gray, “Dispersive white-light interferometry for absolute distance measurement with dielectric multilayer systems on the target”, Optics Letters, Vol. 21, No. 7, pp. 528 to 530) in 1996 since a profile of a four-step grating has been measured by J. Schwider and Liang Zhou (J. Schwider and Liang Zhou, “Dispersive interferometric profilometer”, Optics Letters, Vol. 19, No. 13, pp. 995 to 997) in 1994.
FIG. 2 illustrates a diagram illustrating a measuring apparatus of a thickness and a surface profile of a thin film using an interferometric principle. As illustrated in FIG. 2, it is understood that the measuring apparatus of a thickness and a surface profile of a thin film using an interferometric principle is configured to include a light source 11, a first beam splitter 20, a second beam splitter 23, a first condensing lens 5, a second condensing lens 6, a reference mirror 34, and a detector 4.
According to the measuring apparatus illustrated in FIG. 2, a part of a light source emitted from the light source 11 is reflected by the first beam splitter 20 and the remaining light passes therethrough. The light reflected by the first beam splitter 20 is incident onto the second beam splitter 23. The light reflected by the second beam splitter 23 passes through the second condensing lens 6 and then is reflected by the reference mirror 34 and then reflected by the second beam splitter 23 to be incident onto the detector 4 as second reflected light. In contrast, the light passing through the second beam splitter 23 passes through the first condensing lens 5 to be reflected from the object 1 to be measured and then is incident onto the detector 4 as first reflected light. That is, interference light of the first reflected light and the second reflected light is incident onto the detector 4. The interference light may include both surface profile information and thickness information on the thin film.
FIG. 3 illustrates a perspective view illustrating a structure of a detector configured by an imaging spectrometer. The imaging spectrometer illustrated in FIG. 3 may analyze a light intensity distribution at every wavelength for one line. That is, as illustrated in FIG. 3, the imaging spectrometer 40 is a device which includes a slit 42, a diffractive optical element 43, and a CCD 44 to obtain an image only for one line from an object to be measured and divide the light at every wavelength by the diffractive optical element, thereby obtaining several hundreds of consecutive spectral bands for one line. Therefore, the surface profile and the thickness of the thin film may be measured and analyzed by such an imaging spectrometer.